Comparisons of intermediate filaments (10 nm) from smooth muscles and axons will be done using biochemical and electron-microscopical techniques. In particular, the possible identities of the 63,000 D peptide from squid and 55,000 D peptide from smooth muscle (as well as others) from the two different cell types will be examined. Stereo electron microscopy is being used to determine the nature of the connections between 100 A filaments and microtubules in squid axoplasm.